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J Bacteriol. 1991 October; 173(20): 6406-6410

research-article

LexA protein of Escherichia coli represses expression of the Tn5 transposase gene.

Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907.

ABSTRACT

The LexA protein of Escherichia coli represses expression of a variety of genes that, by definition, constitute the SOS regulon. Genetic evidence suggests that Tn5 transposition is also regulated by the product of the lexA gene (C.-T. Kuan, S.-K. Liu, and I. Tessman, Genetics 128:45-57, 1991). We now show that the LexA protein represses expression of the tnp gene, located in the IS50R component of Tn5, which encodes a transposase, and that LexA does not repress expression of the IS50R inh gene, which encodes an inhibitor of transposition. Elimination of LexA resulted in increased expression of the tnp gene by a factor of 2.7 +/- 0.4, as indicated by the activity of a lacZ gene fused to the tnp gene. LexA protein retarded the electrophoretic movement of a 101-bp segment of IS50R DNA that contained a putative LexA protein-binding site in the tnp promoter; the interaction between the LexA repressor and the promoter region of the tnp gene appears to be relatively weak. These features show that the IS50R tnp gene is a member of the SOS regulon.

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